Fix warning in doctest for Agent.start_link/2
Fix warning in doctest for Agent.start_link/2

gfvcastro/elixir,lexmag/elixir,kimshrier/elixir,beedub/elixir,pedrosnk/elixir,joshprice/elixir,antipax/elixir,ggcampinho/elixir,michalmuskala/elixir,kelvinst/elixir,beedub/elixir,pedrosnk/elixir,kelvinst/elixir,gfvcastro/elixir,ggcampinho/elixir,kimshrier/elixir,lexmag/elixir,elixir-lang/elixir,antipax/elixir